1. Field of the Invention
Embodiments of the invention generally relate to electrochemical plating and, more particularly, to an apparatus for securing a substrate in an electrochemical plating system.
2. Description of the Related Art
Metallization of sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. More particularly, in devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio (greater than about 4:1, for example) interconnect features with a conductive material, such as copper or aluminum, for example. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) have been used to fill these interconnect features. However, as the interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result thereof, plating techniques, such as electrochemical plating (ECP) and electroless plating, for example, have emerged as promising processes for void free filling of sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.
In an ECP process, for example, sub-quarter micron sized high aspect ratio features formed into the surface of a substrate (or a layer deposited thereon) may be efficiently filled with a conductive material, such as copper, for example. ECP processes are generally two stage processes, wherein a seed layer is first formed over the surface features of the substrate, and then the surface features of the substrate are exposed to a plating solution, while an electrical bias is simultaneously applied between the substrate and a copper anode positioned within the plating solution. The plating solution is generally rich in ions to be plated onto the surface of the substrate, and therefore, the application of the electrical bias causes these ions to be urged out of the plating solution and to be plated onto the seed layer.
Typically, the electrical bias is provided to the substrate via one or more electrical contacts. Commonly, the seed layer formed on the substrate may extend from a plating surface around beveled edges of the substrate to a non-plating surface. Accordingly, for different systems, the electrical contacts may be in electrical contact with either the plating surface or the non-plating surface. Regardless of location, it is generally desirable to isolate the electrical contacts, as well as the non-plating surface of the substrate from the plating material, to avoid undesirable plating thereon. Plating on the electrical contacts may alter the resistance of the electrical contacts and have a negative effect on the substrate plating uniformity. Plating on the non-plating surface may result in an extra processing step to remove the plating. The extra processing step may be costly, time consuming and place additional stress on the substrate.
Conventional approaches to isolate the electrical contacts and non-plating surface from the plating solution typically include providing one or more sealing elements to contact the same surface of the substrate as the electrical contacts. For example, sealing members positioned to engage the plating surface may be placed adjacent electrical contacts positioned to contact the plating surface. The sealing members and electrical contacts also provide support for the substrate. However, the combination of the electrical contacts and the associated seals generally takes up several millimeters (generally between 3 and about 7 millimeters) of the perimeter of the plating surface area. Since this surface area is used to make electrical and seal contacts, the area cannot be used to support device formation.
In an effort to utilize this perimeter surface area, some systems may include sealing members positioned to engage the non-plating surface adjacent electrical contacts positioned to contact the non-plating surface. However, without sealing members or electrical contacts on the plating surface to support the substrate, some other means may be needed to support the substrate. Typically, a vacuum is applied to the substrate, to pull the non-plating surface up into contact with the sealing members and electrical contacts. However, the vacuum applied to the substrate may create a stress on the substrate, and may lead to substrate breakage. If the sealing members happen to leak, the vacuum may be unable to maintain the substrate against the electrical contacts with sufficient force and the plating solution may enter the vacuum, causing damage to the vacuum.
Therefore, there is a need for an improved apparatus for securing a substrate in an electrochemical plating system.